Low power consumption is a performance indicator for communication network operators and the users of a cellular phone. The power consumption of a User Equipment (UE) is typically described in terms of battery life time, and more specifically in terms of talk time and standby time. On the network side the power consumption is described as the power consumption of network elements, such as transmission nodes or access nodes, wherein power consumption is measured for different configuration and load situations.
Even if a user is not making a call, the mobile phone consumes power. For example, when being switched on but not making any call, which is also referred to that a UE is in an idle mode, the UE usually searches periodically for its environment, e.g. synchronization sequences, reference signals and downlink broadcast channels or the like (the elements to be searched for are defined in the different communication network standards and may be different depending on the actual type of network). Furthermore, when the UE is in the idle mode, downlink pilot signals may be received, and circuitry is run to detect paging channel information in order to get activated if a call is received.
Recently, the idea that a UE may assist the network in making decisions regarding its configuration for power saving has been adopted. This reflects the understanding that the UE may have greater understanding of the applications running on the device. A single bit has been specified called the power preference indication (PPI) bit.
Radio Resource Control (RRC) is used to handle the control plane signaling of Layer 3 between the UEs and the universal terrestrial radio access network UTRAN, e.g., the evolved Node B's (eNBs) and radio network controllers (RNCs) that make up the UMTS radio access network. RRC signaling includes functions for connection establishment and release, broadcast of system information, radio bearer establishment/reconfiguration and release, RRC connection mobility procedures, paging notification and release, outer loop power control, etc. As a part of RRC, a UE in radio resource control connected mode (RRC_CONNECTED) may initiate the UE assistance information procedure whenever the UE wants to provide information to assist the network in configuring radio resources. The UE initiates the UE Assistance Information procedure by sending the UEAssistanceInformation message. Accordingly, the UE sends a PPI indication in a UEAssistanceInformation message to an access point, e.g., an evolved node B (eNB), to set its configuration to low power consumption (PPI=1) or to normal (PPI=0).
When the UE sends PPI=1, the network may respond with a configuration that is optimized for power saving. Otherwise when the UE sends PPI=0, the network provides a configuration that is optimized to provide the UE with the Quality of Service (QoS) guarantees that the UE requested. However, optimizing for power generally has a detrimental impact on performance, most commonly on the delay performance. When the network provides a configuration optimized for power saving, it is possible that the UE may experience delays in its applications' performance. The idea behind PPI was that the UE would send a request for PPI=1 when it was running delay-tolerant applications, such as background traffic. However, there is nothing to preclude the UE from sending PPI=1 and then running a delay-sensitive application. In this case, certain inconsistencies may arise depending upon whether the network chooses to prioritize the PPI over its QoS guarantees or not.